Piezo-electric crystal apparatus



Jan. 7, 1930. H. D. EISENHAUER PIA'zo ELECTRIC CRYSTAL APPARATUS ng y INVENTOR. zlsefzaMr,

ATTORNEY Patented Jan. 7, 1930 UNITED STATES PATENT oFFIcE HARRY D. EISENHAUER, OIE MOUNT RAINIER, MARYLAND PIEZO-ELECTRIC CRYSTAL APPARATUS Application filed March 21, 1927. Serial No. 177,190.

My invention relates broadly to piezo electric crystal apparatus and more particularly m Another objectof my invention is to provide a piezo electric crystal holder wherein the piezo electric crystal element contacts with the bottom electrode of the holder solely through a central zonethereof leaving the piezo electric crystal element free at opposite ends thereof for unrestricted oscillation along the Y axis. i Y

Another object of my invention is to provide a piezo electric crystal holder in which the friction 1oetween electrodes and the surfaces of a piezo electric crystal element is reduced to a minimum for facilitating the unrestricted vibration of the piezo electric crystal element for the development of constant frequency electrical oscillations.

llfly invention will be more clearly understood from the following' specification lby reference to the accompanying drawings, in which j 'Figure 1 is a plan'view showing the piezo electric crystal holder; Fig. 2 is a cross-sectional view through the piezo electric crystal holder on line 2-2 of Fig. 1; Fig. 3 is a lateral cross-sectional view through the piezo electric crystal holderon line 3-3 of Fig. 2 and Fig. 4 is a cross-sectional view through the piezo electric crystal holder on line 1 -4 of Fig. 1.

The piezo electric crystal holder of my inlow frequency piezo electric crystals, that is, crystals which oscillate at frequencies within a range of 10-100 lrilocycles. I have found Cthat low frequency crystalsv having a Y or 15 lateral axis vibration will not oscillate very` readily when placed in a holder having the this sluggishness is due to the friction which vention is particularly adapted for use with exists between these surfaces when the crystal is oscillating. In the piezo electric crystal apparatus of my invention, I reduce the friction between the electrode and the surfaces of the piezo electric crystal element to a minimum allowing unrestricted vibration of the piezo electric crystal element along the 'lateral or Y axis thus increasing its piezo electric properties.

Referring to the' drawings in more detail,

reference character 1 designates the lower electrode of the piezo electric crystal holder. Reference character 2 represents an insulated housing which is positioned upon the lower electrode 1.v A top closure 3 is provided for the insulated housing 2. The upper electrode 4 is secured to the top closure 3 by means of sets of screws or-'other suitable means 5.,

rIhe upper electrodel is provided with a termina'l (i which passes through the top 3 for establishing an electrical connection for the piezo electric crystal device exterior of the casing. Screw members fare provided securing the upper portion 3 with respect the lower plate 1. In order tc center 'r piezo electric crystal member 8 within the piezo electric crystal holder, I provide screw members 9 which engage screw threaded apn ertures in the lower plate 1. An eccentric device 10 may be provided on one of the end screw members 9 and shiftedin position for properly centering the piezo electric crystal member 8 while not restricting the free mel chanical vibrationthereof. The upper electrode l is centrally positioned over the piezo electric crystal member 8 but is vseparated from the upper surface .thereof by a positive air gap 11 allowing the free upper-movement of the piezo electric crystal element '8 while providing a 4capacitive connection with `the upper surface thereof. The lower electrode 1 is provided with a' central zonel which I have indicated between the 'dimensions' X-X Vwhich is inthe nature of 'a plateau or high flat surface in the center ofthe bottom electrode. This surface is substantially flat throughout the central zone. and then tapers f v0H in a plane represented at 12'and in a dfferent plane represented at 13, these two 'planes theoretically meeting Aat an apex at substantially the center of the piezo electric crystal holder. Byreason of the tapered off surfaces 12 and 13, a free air surface which I have represented at 14 is provided under the ends of the crystal 8. This free air space 14 permits unrestricted oscillationof the piezo electric crystal element 8 along the lateral or Y axis, thus increasing the effective piezo electric crystal properties. The upper electrode may rest on the crystal or may be separated by the air gap 11 which is approxi I have found that by use of thepresent type of piezo electric crystal holder that it has been possible to make two out of eight crystals oscillate with a type of holder where the contact electrodes are either in intimate contact or with one electrode spaced from one surface of the piezo electric crystal whereas when the same crystals are vplaced in the holder of the vpresent invention, all of the eight crystals produced sustained oscillations of constant frequency. I find that substantially more output can be obtained when using the piezo electric crystal apparatus of my present invention than is possible in piezo electric crystal holders heretofore available in the art.

While I have described the crystal holder of my inventionin one of its preferred embodiments, I desire it to be lunderstood that modifications may be made and that no limitations are intended other than are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of theUnited States is as follows: 4

1. A piezo electric crystal holder comprising a pair of electrodes, a piezo electric crystal, means for spacing one of said electrodes from one surface of said piezo electric crystal, the other' of said electrodes haying a flattened Central Zone and side zones slightly inclined to said flattened central zone, said flattened central zone being adapted to contact with a surface of said piezo electric crystal.

2. A piezo electric crystal holder comprising a-fpair of electrodes, a housing positioned upon one vof said electrodes, means for supporting the other of said electrodes from said housing, a piezo electric crystal element, means for centering said piezo electric crystal element within said housing, said first mentioned electrode having a raised and flattened central zone for supporting said piezo elec- 'tric crystal element out of contact with the surfaces of said electrodes on opposite sides of said flattened central zone.

3. A piezoI electric crystal holder comprising a pair of parallel electrodes, means on the lower of said electrodes for centering a piezo electric crystal element between said electrodes, a flattened central zone on said lower electrode for supporting said piezo electric crystal element substantially-out of Contact with the extremities of said lower electrode on opposite sides of the flattened central zone thereof.

4L. A piezo electric crystal apparatus comprising a conductive base member, a housing carried by said base member,- an uppper electrode carried by said housing, a piezo electric crystal element'located-between said upper electrode and said basemember, said base member being attened in the central portion thereof and tapered on .opposite sides of the flattened portion at substantially obtuse angles with respect to the plane of the flattened central portion thereof whereby said piezo electric crystal element contacts with said base member through a central zone thereof and is free to vibrate without restriction between said electrodes.

5. Piezo electric crystal apparatus comprising a base member having a raised and flattened central portion, means disposed about the sides and at the ends of said base member for adjustably centering a piezo electric crystal element with respect to said base member with one face of said crystal element in contact with the raised and flattened central portion of said base member, a housing positioned on said base member, an electrode carried by said housing in spaced relation to the upper surface of said piezo electric crystal whereby said piezo electric crystal element is free to vibrate without restriction.

6. Piezo electric crystal apparatus comprising a metallic electrode having a flat surface at its central portion and surfaces inclined with respect to and merging into said centrally disposed flat surface, said last mentioned surfaces of said electrode extending to the edges thereof. a piezo electric crystal supported upon said flat surface with portions of said piezo electric crystal element out of Contact with the inclined surfaces of said metallic electrode, a housing, a second electrode positioned within said housing for establishing a connection with the upper surface of said piezo electric crystal element whereby said piezo electric crystal element is free to vibrate without restriction between said electrodes.

7. In a piezo electric crystal apparat-us, a housing, a lower electrode, an upper electrode, a'piezo electric crystal element arranged to be centered between said electrodes and an ecposed plane centric member within said housing for adjustin the position of said piezo electric crysta l element within said housing.

8. In a piezo electric crystal holder, an electrode having a centrally disposed plane flat surface and a plurality of surfaces merging into said first named surface but being slightly inclined thereto, said centrally disfiat surface being adapted to a surface of a piezo electric HARRY D.. EISENHAUER.

contact with crystal. 

